js原生方法reduce实现

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    <title>reduce</title>

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<body>

    <script>

        Array.prototype.my_reduce = function (callback, initialValue) {

            if (!Array.isArray(this) || !this.length || typeof callback !== 'function') {

                return []

            } else {

                // 判断是否有初始值

                let hasInitialValue = initialValue !== undefined;

                let value = hasInitialValue ? initialValue : tihs[0];

                for (let index = hasInitialValue ? 0 : 1; index < this.length; index++) {

                    const element = this[index];

                    value = callback(value, element, index, this)

                }

                return value

            }

        }

        let arr = [1, 2, 3, 4, 5]

        let res = arr.my_reduce((pre, cur, i, arr) => {

            console.log(pre, cur, i, arr)

            return pre + cur

        }, 10)

        console.log(res)//25

    </script>

</body>

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js原生方法reduce实现

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